On your laptop, there's a CRT/External Display button (to activate it you might have to use the Fn key). Typically, there's 3 modes that button switches between:
1. Laptop Screen Only
2. External Screen Only
3. Same image on both Screens
(not necessarily in that order)
One thing you have to keep in mind is that in order for the 3rd option to work your projector needs to be able to show/handle the resolution of your laptop screen since you will be sending the same signal to both. (if you projector cannot handle the laptop screen resolution it will simply show nothing. So to try to fix that set your laptop screen resolution to the one the projector can handle and try connecting then)
Please ask if you have more questions. if you do though, please provide the laptop make and model and the projector make and model
i have a sort of similar problem i was hoping you could help with. i am trying to set my laptop for the external monitor, and i have no problems doing that. my problem lies in that the very sides of my screen are cut off as if my laptop thinks my television is bigger than it is. my laptop is a HP Pavilion dv6 and my tv is an ELEMENT. do i just need to change my laptop res? and if so, how do i do that?